fix(ssr): make the render timeout cover rendering

[bobzhang]

Fixes #173.

App::render's timeout could never fire. All of SSR's async work — graph evaluation, drain_task, the HTTP fetches create_resource issues — happens inside @runtime.SSRHost(...), on the line before with_timeout. What with_timeout wrapped was render_to_string, declared pub fn rather than pub async fn, so it has no suspension point and the timer can never preempt it.

This moves the SSRHost construction inside the timeout, where the awaiting actually is, and keeps defer host.cleanup() in the same closure so it still runs on both the success and the cancelled path.

 let (origin, path) = split_url(url)
-let host = @runtime.SSRHost(origin~, path~, () => {
-  let output = (self.builder)()
-  output.0.map(html => html.0)
-})
-defer host.cleanup()
-let html = @async.with_timeout(timeout, () => {
-  host.render_to_string(head.map(html => html.to_virtual_dom()))
-})
-html
+@async.with_timeout(timeout, () => {
+  let host = @runtime.SSRHost(origin~, path~, () => {
+    let output = (self.builder)()
+    output.0.map(html => html.0)
+  })
+  defer host.cleanup()
+  host.render_to_string(head.map(html => html.to_virtual_dom()))
+})

Verification

Probe in #173 — render against an endpoint that sleeps 2s, with timeout=100:

	result
rabbita@0.15.6	RETURNED (no raise) after ~2s, with the fetched data
this branch	RAISED: TimeoutError

Cancellation does not leak the host: with SSRHost::cleanup instrumented with a println, the timeout path prints [probe] SSRHost::cleanup ran before the raise.

• moon check --target native --deny-warn — pass
• moon check --target wasm --deny-warn — pass
• moon test --target native — 86 passed, unchanged

Two things I deliberately did not do

No regression test. @cmd.perform and @cmd.effect are #cfg(target="js"), so the native async-command surface is effectively HTTP and a test needs a live server. moon test is also commented out in check.yml, so it would not run in CI anyway. Rather than add a timing-sensitive test nobody runs, the reproduction is written out in full in #173 so it can be verified independently.

No version bump. Left at 0.15.6 so the bump can be made at release time rather than going stale while this is reviewed.

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https://claude.ai/code/session_01AmoyPMELemz5hdNNdXyAkm